#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 101;
char q[N], p[N];

void turn(char& n)
{
    if (n == '*') n = 'o';
    else if (n == 'o') n = '*';
}

int main()
{
    cin >> q >> p;
    int ans = 0;
    for (int i = 0; i <= sizeof(q); ++i)
    {
        if (q[i] != p[i])
        {
            turn(q[i]), turn(q[i + 1]);
            ans++;
        }
    }
    cout << ans << endl;
    return 0;
}